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8N 12v conversion with battery drain

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elvin estes

02-14-2000 18:09:09




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I purchased an 85% restored 1949 8N which had a 12v conversion. The 15% not restored consisted mainly of old wiring. It runs and looks great but the new battery drains every day if the + cable is left connected. I believe part fo the problem is the old wiring may have shorted the alternator. Is there a schematic to show correct wiring when a 12v conversion is added so I can make sure the wiring was done correctly. The conversion did not look like a kit . Thanks ... Elvin

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Phil (NJ)

02-15-2000 11:42:11




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 Re: 8N 12v conversion with battery drain in reply to elvin estes, 02-14-2000 18:09:09  
Elvin, If you have current drain from you battery, with the ignition switch off, that is enough to discharge your battery in a day.

1. Alternator diode/diodes may be shorted.

2. Incorrect Wiring of alternator, excite term may be connected to Battery. Normal to have a diode (FWD) to the switched side of the ignition switch.

3. Bad Ignition Switch (hi-res short)

4. Starting Selenoid is drawing Current. This can be through the contacts or the relay coil.

Hope this helps, Phil

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Bob W [FL]

02-15-2000 04:51:50




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 Re: 8N 12v conversion with battery drain in reply to elvin estes, 02-14-2000 18:09:09  
Go to the link below and scroll down. There is a 12 volt diagram. I used a 10 OHM 10 Watt resistor
(from Radio Shack)instead of the indicator lamp. Or use can use a Diode as tOTG suggested. I used this diagram on mine and it works fine.



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tOTG

02-14-2000 18:12:52




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 Re: 8N 12v conversion with battery drain in reply to elvin estes, 02-14-2000 18:09:09  
With the limited information you've provided, I'd guess that you need a diode (1A, 50V, $.49 at Ratshack) in the exciter circuit.

John.CO



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Phil (NJ)

02-15-2000 07:11:53




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 Re: Re: 8N 12v conversion with battery drain in reply to tOTG, 02-14-2000 18:12:52  
John,
"I'd guess that you need a diode (1A, 50V, $.49 at Ratshack) in the exciter circuit".

When using a diode for exciting an Inductive Load the "in-rush" current is the specification you should define. Should be XXX Amps for XX nsec, most power diodes would meet requirement, not sure
a Radio Shack 1 amp has those characteristics.

JMHO



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EricG.NH

02-16-2000 05:02:56




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 Re: Re: Re: 8N 12v conversion with battery drain in reply to Phil (NJ), 02-15-2000 07:11:53  
"In rush" current? Isn't "in rush" current more associated with capacitive loads? I thought inductors and inductive loads RESIST changes in current. Which is why a backbiased or free-wheeling diode is needed on a switched, inductive load. It provides a place for the current to go rather than through the switch or relay. The abrupt change in current, causes a very large reverse voltage to appear across the inductor and then the switch. The inductor, wants to resist the change and maintain the current. The diode gives the current an "out". It's this very large reverse voltage that drives the choice of diode. Maybe that's what your thinking of.
In rush current, occurs on systems at power up or when switching. Initially capacitors look like short circuits, producing high initial currents that taper off. Inductors look like opens at power up, and consequently have very low initial currents. Hope I haven't poked any eyeballs.
Eric
P.S. John, EE doesn't have to be boring. Ask me some time about some of the defense programs I've worked on. It can actually get kinda interesting. Not quite as fun as tractorin' but different every day. :o)

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Phil (NJ)

02-16-2000 07:14:06




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 Re: Re: Re: Re: 8N 12v conversion with battery drain in reply to EricG.NH, 02-16-2000 05:02:56  
Eric, One of the most important specification when driving analog devices, with silicon, is the "Forward Surge Current". Inductive spikes in the "NEGATIVE" are particularly troublesome to diodes.

i.e. 1n4001 1 amp Cont., 50amp Ifsm, 50V vrpm

i.e. 1n5402 3 amp Cont., 200amp Ifsm, 200v vrpm

Which One would You Spec for driving an Alternator ??

Those that think pure inductive or pure capacitive loads exist are theorists who have never practiced in the real world. He who has not under spec'd a diode (just didn't expect that spike) should cast the first stone.

JMHO

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EricG.NH

02-17-2000 05:01:06




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 Re: Re: Re: Re: Re: 8N 12v conversion with battery drain in reply to Phil (NJ), 02-16-2000 07:14:06  
Given the un-switched, predominately inductive load in the alternator field circuit I'd choose the 1N4001. Considering this and the success this part has had in this application, the actual "in-rush" or "forward surge current" and reverse voltages are likely small. But I've never measured it in this case and I usually yield to experience. I can be taught! What is it for the field input of a typical, self exciting alternator?
Of course, if there was no big cost difference or availability issue, go with a beefier part. And yes, I've under spec'd and OVER spec'd diodes in the past. And yes, I've been bitten by voltage spikes when switching MOSTLY inductive loads and current spikes when switching MOSTLY capacitive loads. And no, I'm not a theorist or a realist, I'm both!
Eric

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tOTG

02-15-2000 11:59:37




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 Re: Re: Re: 8N 12v conversion with battery drain in reply to Phil (NJ), 02-15-2000 07:11:53  
I'm not an electrical engineer...the work would bore me. Is XX nsec something from a porn web site?

I've made dozens of these 12V conversions and the diode specified will work. But Phil, if my $.49 solution is too much for elvin to risk, how about you engineer him the right fix.

John.CO



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Phil(NJ)

02-15-2000 12:17:38




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 Re: Re: Re: Re: 8N 12v conversion with battery drain in reply to tOTG, 02-15-2000 11:59:37  
John, Didn't mean to poke a stick in your eye. Just that there are lots of diode types at radio shack and 1 amp is "down" close to signal class. It would be helpful have a part number, of the one, that you know works. Phil,



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tOTG

02-15-2000 17:41:38




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 Re: Re: Re: Re: Re: 8N 12v conversion with battery drain in reply to Phil(NJ), 02-15-2000 12:17:38  
Cat. No. 276-1101A
50V, 1A
MICROMINI
SILICON DIODES (2)
1N4001



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